Cholesterol is well known as a main etiologic factor for arteriosclerosis that causes severe heart diseases. Especially, increased levels of serum low density lipoprotein (LDL) are believed to be a definite risk factor for coronary heart diseases (CHDs). Remedies for decreasing the level of LDL-cholesterol (LDL-C) in plasma by use of statins have been shown to be clinically effective in preventing the onset of CHDs and improving the conditions of CHDs and survivals in patients suffering from hypercholesterolemia. However, about 40% of CHDs patients have a normal level of LDL-C, and are not always cured effectively by remedies for decreasing the level of LDL-C. On the other hand, it has been known that a half of CHDs patients having a normal level of LDL-C shows a lower level of high density lipoprotein (HDL) cholesterol (HDL-C).
Recently, the lower level of serum HDL-C has been shown to be an additional risk factor of the onset and the recurrence of CHD.
HDL plays an important role in reverse cholesterol transport system that is known as a biological mechanism to transfer an excess cholesterol in cells back to liver so as to maintain the level of cholesterol in living bodies normally.
Lipoproteins such as HDL is mainly comprised of lipids and proteins called apoprotein, and HDL comprises an apoprotein as referred to apolipoprotein AI (hereinafter, made up by apoAI) as a main component.
Excess free cholesterols (FCs) and phospholipids in peripheral cells are extracted by free apoAI to form lipoproteins called preβ-HDL(s). The excess FCs integrated in the preβ-HDLs are transformed into cholesteryl esters (CEs) by lecithin: cholesterol acyl transferase (LCAT), while the preβ-HDLs increase in their particle size to mature into spherical HDLs (HDL3s). The matured HDLs are classified into diverse subfractions based on the density, and these particles further grow up to form HDL2(s). CEs are continuously transferred into very low density lipoprotein (VLDL) and LDL by means of cholesteryl ester-transporter protein (CETP). Those lipoproteins that integrate CEs are finally taken into the liver via receptors. During the course, apoAI is regenerated, and again interacts with peripheral cells to repeat the extraction of cholesterols and the regeneration of preβ-HDLs.
It has been well understood that HDL plays a central role in reverse cholesterol transport system and is a defensive factor of arteriosclerosis. It is expected that agents that promote the HDL functions could be clinically effective as medicaments for treating arteriosclerotic diseases. Accordingly, studies to develop agents that enhance the level of HDL in plasma have been conducted via various approaches.
Among them, one of the most promising approaches is to enhance the serum level of apoAI, a main component of HDL. It is acknowledged that apoAI production increased by enhancing the expression of apoAI gene leads to directly the elevation of HDL-C level in plasma, resulting in the activation of reverse cholesterol transport system. In fact, it has been demonstrated that the mRNA level of apoAI in liver correlates closely with the levels of apoAI and HDL-C in blood (Dueland S., France D., Wang S L., Trawick J D., and Davis R A., J. Lipid Res., 38:1445-53 (1997), “Cholesterol 7 alpha-hydroxylase influences the expression of hepatic apoA-I in two inbred mouse strains displaying different susceptibilities to atherosclerosis and in hepatoma cells.”). In addition, it has been shown that apoAI-transgenic mice and rabbit pathologic models administered with apoAI exhibit anti-arteriosclerosis activities (Rubin E. M., Krauss R. M., Spangler E. A., Verstuyft J. G., and Clift S. M., Nature 353, 265-267 (1991), “Inhibition of early atherogenesis in transgenic mice by human apolipoprotein AI.”; Plump A. S., Scott C. J., Breslow J. L., Proc. Natl. Acad. Sci. USA., 91, 9607-9611 (1994), “Human apolipoprotein A-I gene expression increases high density lipoprotein and suppress atherosclerosis in the apolipoprotein E-deficient mouse.”; Miyazaki A., Sakuma S., Morikawa W., Takiue T., Miake F., Terano T., Sakai M., Hakamata H., Sakamoto Y., et al., Arterioscler. Thromb. Vasc. Biol., 15, 1882-1888 (1995), “Intravenous injection of rabbit apolipoprotein A-I inhibits the progression of atherosclerosis in cholesterol-fed rabbits.”).
All these facts clearly suggest that agents that enhance the expression of apoAI would be candidates for medicaments of dyslipidemia, arteriosclerotic diseases, and other diverse diseases associated with HDL.
Compounds that increase apoAI are described in Japanese Patent Publication (kokai) No. 221959/1993, Japanese Patent Publication (kokai) No. 291094/1996, and WO97/09048, but those compounds are different from the compounds according to the present invention in terms of chemical structure.
Structurally similar compounds to those described in the invention have been disclosed in WO97/32574, Japanese Patent Publication (kokai) No. 175965/1989, Japanese Patent Publication (kokai) No. 34967/1991, Tet. Lett., 1974, 36, 3151, Japanese Patent Publication (kokai) No. 50930/1992, Collect. Czech. Chem. Commun., 1975, 40, 1892, WO96/39387, WO98/52941, WO99/02497, and U.S. Pat. No. 5,919,970, however an activity to enhance the expression of apoAI has not been described.